The structures, properties, and metabolism of bilirubin photoisomers and bilirubin photoproducts and the mechanism of phototherapy for neonatal jaundice will be investigated using the Gunn rat as a model for the jaundiced patient. The investigation will include measurements of the therapeutic potential of current light sources and the action spectrum for phototherapy. In addition, the mechanism of bilirubin conjugation and excretion will be studied by examining the biliary excretion and hepatic metabolism of synthetic model compounds in rats. The research will involve chemistry, biochemistry and photobiology and it will provide valuable information for improving the safety and effectiveness of phototherapy and for understanding and diagnosing liver disease.